Shearer took to Twitter to claim that the lawyer of producer James L Brooks explained the "show will go on, Harry will not be part of it, wish him the best".
"This because I wanted what we've always had: the freedom to do other work. Of course, I wish him the very best," he wrote.
"Thanks, Simpsons fans, for your support," he added.
Shearer has been with the show - which was recently renewed for a 26th and 27th run - since it began in 1989.